As a renewable fuel, biodiesel has become an attractive alternative for a diesel fuel substitute. Since the 1990s, vegetable oil has been the major source for global biodiesel production. Biodiesel-alternative fuel makes inroads but hurdles remain. For example, soybean oil was the largest biodiesel feedstock in the U.S. for the past several years. However, despite the wide use of vegetable oil as a feedstock for the production of vegetable oil, its high cost has limited the viability of biodiesel as a competitive fuel. For vegetable-oil based biodiesel, the feedstock alone amounts to about 70-80% of the total production cost.